minimum period (of study) required (to complete the degree / for the BA/MA/PhD/etc. degree)
minimum (number of) semesters required
etc.

I'm not sure 'duration' is exactly wrong, and 'studies' might be possible in BE, but neither of those is what I would say.

'Study period' would not be right in AE, because it means 'study' in the sense of 'lernen' -- something like Hausaufgabenbetreuungsstunde.